Treated wood material

ABSTRACT

The present disclosure describes a treated cellulosic material comprising: a cellulosic material having a porous structure defining a plurality of pores, at least a portion of the pores containing a treating agent comprising: a polymer comprising an olefin-carboxylic acid copolymer; and a modifying agent comprising a quat.

BACKGROUND OF THE INVENTION

Porous materials, such as cellulosic materials, need to be protected from mold growth, insect attack, rot and water impregnation to help preserve the physical properties of the cellulosic material. One example of such a cellulosic material is wood. A variety of treatment agents and preservation methods are known to preserve cellulosic materials.

Modern preservation methods typically involve pressure treating the cellulosic material with a treating agent. Pressure treatment typically allows the treating agent to penetrate throughout the porous structure of the cellulosic material. The treating agent is typically a chemical compound selected to impart the desired physical properties to the cellulosic material. For example, treating agents that increase hardness, add water resistance and improve the dimensional stability of the cellulosic material are of interest. Wood is capable of absorbing as much as 100% of its weight in water which causes the wood to swell, which after loss of water through evaporation causes the wood to shrink. This process of water absorption/evaporation is non-uniform and creates internal stresses in the wood leading to splitting, warping, bowing, crooking, twisting, cupping, etc. Also, water can serve as a pathway for organisms that degrade the cellulosic material, such as insects or fungus. Treating agents that repel insects, or minimize the formation of fungi/molds, or improve the overall durability of the cellulosic material are of interest. Further, treating agents can improve wind resistance, ultraviolet radiation resistance, stability at high and low temperatures, pest resistance, mold resistance, fire resistance and other issues which might affect the physical properties of the cellulosic material.

Termites are one of the most significant insect groups responsible for wood damage. In order to mitigate termite damage, the use of naturally durable wood species, preservative treatments, and engineered wood products have been employed. However, the need for improved technologies for termite resistance are desirable due to the limited availability of durable woods, the high percentage weight gains required for preservatives to provide efficacy, and the “unnatural” look of engineered wood. A technology which is provides termite resistance and dimensional stability to wood is highly desirable.

One compound used to treat wood is quaternary ammonium compounds, referred to herein as quats. Quats are known to add insect and fungi resistance to wood. Quats are also known to dissociate from wood, and can be a skin and respiratory irritant and cause harm to aquatic systems. Another disadvantage to quats is they can behave as surfactants and make wood exposed to rain pick up moisture more easily.

An improved treating agent for cellulosic materials is desired. In particular, a treating agent which prevents dissociation of quats from the cellulosic material while still maintaining good insect and fungi resistance is desired. Additionally, improved dimensional stability when using quats is desired.

SUMMARY OF THE INVENTION

The present disclosure describes a treated cellulosic material comprising: a cellulosic material having a porous structure defining a plurality of pores, at least a portion of the pores containing a treating agent comprising: a polymer comprising an olefin-carboxylic acid copolymer; and a modifying agent comprising a quat.

The present disclosure further describes a method for preparing a treated cellulosic material comprising: providing a cellulosic material; a first treatment protocol comprising impregnating the cellulosic material with an aqueous dispersion comprising a polymer, the polymer comprising an olefin-carboxylic acid copolymer; and a second treatment protocol comprising impregnating the cellulosic material with a modifying agent, the modifying agent comprising a quat.

DETAILED DESCRIPTION OF THE INVENTION

A “treated cellulosic material” is a cellulosic material that has been treated with a treating agent to modify the properties of the cellulosic material. The properties modified by the treating agent include, but are not limited to, increased hydrophobicity, dimensional stability, fungi resistance, mold resistance, insect resistance, hardness, surface appearance, UV stability, fire resistance, and coatability. Increasing the hydrophobicity of a cellulosic material can provide other ancillary benefits, such as dimensional stability, by reducing the rate of water adsorption and evaporation, thus reducing the internal stresses of expanding and contracting.

A “treating agent” is a substance that, when combined with the cellulosic material, modifies the properties of the cellulosic material. In one instance, the treating agent comprises both a polymer and a modifying agent. The treating agent is applied to the cellulosic material. One method of applying the treating agent to the cellulosic material is through impregnation using pressure treatment. In one instance, the polymer is applied to the cellulosic material as part of a dispersion. Other methods of applying the treating agent are known, such as brushing, coating, spraying, dipping, soaking and extrusion. Once applied, the treating agent will permeate at least a portion of the pores of the cellulosic material.

A treating agent is a substance that, when combined with the cellulosic material, modifies the properties of the cellulosic material. In one instance, the treating agent comprises both a polymer and a modifying agent. The treating agent is applied to the cellulosic material. One method of applying the treating agent to the cellulosic material is through impregnation using pressure treatment. Other methods of applying the treating agent are known, such as brushing, coating, spraying, dipping, soaking and extrusion. Once applied, the treating agent will permeate at least a portion of the pores of the cellulosic material.

As used herein, polymer refers to a molecule that is formed from one or more types of monomers. The polymer is preferably a copolymer or a mixture of copolymers and polymers. As used herein, copolymer may refer to an alternating copolymer, a periodic copolymer, a statistical copolymer, a random copolymer, a block copolymer, a graft copolymer, or other copolymer as is known. As used herein, copolymer refers to a polymer formed by uniting two or more monomers. Examples of copolymers include bipolymers, terpolymers, tetrapolymers, and other higher-ordered copolymers. In one instance, the polymer comprises an olefin-carboxylic acid copolymer. In one instance, the olefin-carboxylic acid copolymer comprises, in polymerized form, a monomer selected from the group comprising ethylene, propylene, 1-butene, 3-methyl-1-butene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-heptene, 1-hexene, 1-octene, 1-decene, 1-dodecene, butadiene, styrene, (meth)acrylic acid, maleic acid, maleic anhydride, or a mixture thereof. In one instance, a styrene acrylic acid dispersion is suitable, for example, Orotan™ CA-2005, commercially available from The Dow Chemical Company. Other suitable polymers and/or copolymers present in the mixture include elastomers, plastics and fibers.

In certain embodiments, the polymer comprises a polar olefin polymer, having a polar group as either a comonomer or grafted monomer. As used herein, a polar olefin polymer is an olefin (co)polymer which contains one or more polar groups. In exemplary embodiments, the polymer may, for example, comprise one or more polar polyolefins, having a polar group as either a comonomer or grafted monomer. Examples of polar groups include carboxylic acids, carboxylic acid anhydrides, carboxylic acid esters, carboxylic acid salts, and carboxylic acid amides. Exemplary polar polyolefins include, but are not limited to, ethylene/acrylic acid (EAA) and ethylene/methacrylic acid (EMAA) copolymers, such as those available under the trademarks PRIMACOR™, commercially available from The Dow Chemical Company, NUCREL™, commercially available from E.I. DuPont de Nemours, and ESCOR™, commercially available from ExxonMobil Chemical Company. Exemplary copolymers also include ethylene/maleic anhydride copolymer, such as those available from The Dow Chemical Company under the trademark AMPLIFY™ GR. Exemplary copolymers further include ethylene/maleic anhydride and propylene/maleic anhydride copolymers, such as those available from Clariant International Ltd. under the trademark LICOCENE™. Other exemplary base polymers include, but are not limited to, ethylene/vinyl acetate copolymer, ethylene/ethyl acrylate (EEA) copolymer, ethylene/methyl methacrylate (EMMA) copolymer, and ethylene butyl acrylate (EBA) copolymer.

Other olefin-carboxylic acid copolymers may also be used as the polymer. Copolymers which have ester or anhydride functionalities can be converted to carboxylic acids or the polymer could also be derived by chemical modification of functional carboxylic acid salts by methods known to one skilled in the art. The polymer can also be modified to form other functional groups such as esters or amides and the like. Those having ordinary skill in the art will recognize that a number of other useful polymers may also be used.

In one embodiment, the base polymer may, for example, comprise a polar polyolefin selected from the group consisting of ethylene/acrylic acid (EAA) copolymer, ethylene/methacrylic acid copolymer (EMAA), and combinations thereof. In one instance, the polymer comprises ethylene/(meth)acrylic acid copolymer either alone, or in a mixture with other polymers or copolymers.

As used herein, the use of the term “(meth)” followed by another term such as acrylate refers to both acrylates and methacrylates. For example, the term “(meth)acrylate” refers to either acrylate or methacrylate; the term “(meth)acrylic” refers to either acrylic or methacrylic; and the term “(meth)acrylic acid” refers to either acrylic acid or methacrylic acid.

In one instance, the polymer is a constituent part of an aqueous dispersion. In one instance, the dispersion is a medium that comprises the polymer, water and one or more organic solvents. The aqueous dispersion is prepared such that the suspended particle size in the dispersion is suitable for penetrating the pores of the cellulosic material for distribution through the cellulosic material. In one instance, the dispersion also comprises one or more additives. In one instance, any solids present in the aqueous dispersion are held in a stable suspension and are transportable by the dispersion into the pores of the cellulosic material. In one instance, the solid content of the dispersion is 1 to 75 weight percent. In one instance the organic solvent is an oxygenated solvent, a hydrocarbon solvent, a halogenated solvent, or a combination thereof.

The carboxylic acid portion of the polymer is neutralized with a neutralizing agent at least in part to form a stable aqueous dispersion. As used herein, a neutralizing agent is any material in which the reaction with the carboxylic acid can potentially result in the formation of a salt. In one instance the neutralizing agent is selected from the hydroxides of alkali metals, ammonia or organic derivatives thereof (including amines). In one instance the neutralizing agent is a strong base or a weak base. For example, the neutralizing agent may be sodium hydroxide, potassium hydroxide, or ammonia or an amine, such as monoethanolamine (MEA), triethanolamine (TEA), diethylethanolamine (DEEA) or dimethylaminoethanol (DMEA). A stable dispersion is a dispersion that is suitable for penetrating the pores of the cellulosic material. The neutralizing agent neutralizes at least a portion of the carboxylic acid groups of the polymer. As used herein, neutralization of the carboxylic acid groups refers to any reaction in which the hydrogen of the carboxylic acid group is transferred. In one instance, 5 to 100 mole percent of the carboxylic acid groups of the polymer are neutralized by the neutralizing agent. In another instance 10 to 80 mole percent of the carboxylic acid groups are neutralized by the neutralizing agent. In still another instance 20 to 70 mole percent of the carboxylic acid groups are neutralized by the neutralizing agent.

The modifying agent is a substance that, when combined with the polymer, increases the hydrophobicity, dimensional stability and insect resistance of the cellulosic material. In one instance, the modifying agent is a quaternary ammonium compound comprising a quaternary ammonium cation and an anion, and is referred to herein as a quat. Suitable modifying agents include quaternary ammonium compounds. Examples of suitable quaternary ammonium compounds include but are not limited to, those having the formula R¹R²R³R⁴N⁺X where R¹, R², R³, and R⁴ independently are carbon substituents which are linear, branched, cyclic or any combination thereof saturated or unsaturated and X is an anion. The sum of the number of carbon atoms in R¹, R², R³, and R⁴ broadly ranges from about 8 to 50. R¹, R², R³, and R⁴ may be alkyl, alkenyl, alkynyl, cycloalkyl, aryl, or any combination of these, and the anion X may be chloride, bromide, iodide, borate, carbonate, bicarbonate, nitrite, or a carboxylate such as acetate, laurate or stearate. Examples of suitable modifying agents include trimethyl soya alkyl ammonium chloride, or an alkyl trimethyl ammonium chloride/bromide (where alkyl can be C12, C16, C18, C12, Coco, palmacyl), or a dialkyl dimethyl ammonium chloride/bromide (where alkyl can be —C8, C10, C12, C16, C18, Hydrogenated Tallow), or an alkyl dimethyl benzyl ammonium chloride/bromide (where alkyl can be C12, C14, C16, C18, Coco), or a mixture thereof.

The treating agent is combined with the cellulosic material. In one instance, the treating agent is introduced to the cellulosic material by pressure treatment, as described herein. In another instance, the treating agent is introduced to the cellulosic material by other techniques known in the art, for example, brushing, coating, dipping, soaking, spraying, and extrusion. The treating agent becomes impregnated in at least a portion of the pores of the cellulosic material, and thereby increases the weight of the cellulosic material. In one instance, the polymer increases the weight of the cellulosic material by 1 to 80 percent (as calculated after drying the cellulosic material). In one instance, the treating agent—the combination of the polymer and the modifying agent—increases the weight of the cellulosic material by 5 to greater than 100 percent (as calculated after drying the cellulosic material).

In one instance, the treating agent comprises one or more additives. The additive may be included as part of the dispersion, as part of the modifying agent, or may be included separately therefrom. Additives which are known to add properties to treated cellulosic materials are suitable, such as, flame retardants, dispersants and/or dyes. For example, the additives may be organic compounds, metallic compounds, or organometallic compounds. In one instance, the additive is a material which improves the wetting or penetration of the polymer into the wood, for example, solvents or surfactants (anionic, cationic or nonionic) that are stable in the dispersion. Examples of additives include, solvents, fillers, thickeners, emulsifiers, dispersing agents, buffers, pigments, penetrants, antistatic agents, odor substances, corrosion inhibitors, preservatives, siliconizing agents, rheology modifiers, anti-settling agents, anti-oxidants, other crosslinkers (e.g. diols and polyols), optical brighteners, waxes, coalescence agents, biocides and anti-foaming agents. Such waxes may include petroleum waxes, paraffin waxes, a natural wax, or a synthetic wax such as polyethylene wax or oxidized polyethylene wax, beeswax, or slack wax. In addition, the treating agent may be used in conjunction with wood preservatives containing, for example, cupric-ammonia, cupric-amine, cupric-ammonia-amine complexes, quaternary ammonium compounds, or other systems. For example, the treating agent may be used with Alkaline Copper-Quaternary ammonium (ACQ) preservative systems. The treating agent may also be used with wood preservative technologies which use zinc salts or boron containing compounds. Optionally, other additives such as insecticides, termiticides, fungicides, and moldicides may be added to the treating agent. In one instance, the additive is included as part of the dispersion and forms a stable suspension therewith. In one instance, one or more surfactant is added to the dispersion. In one instance, a surfactant is selected which reduces gelling of the polymer at the surface of the cellulosic material. In one instance, a surfactant is selected which increases the amount of polymer impregnated in the cellulosic material. For example, suitable surfactants may be nonionic, anionic, or cationic. Examples of nonionic surfactants include: alkoxylated alcohols, alkoxylated alkyl phenols, fatty acid esters, amine and amide derivatives, alkylpolyglucosides, ethylene oxide/propylene oxide copolymers, polyols and alkoxylated polyols. For example, a nonionic surfactant is TERGITOL™ L-62, commercially available from The Dow Chemical Company. Examples of anionic surfactants include: alkyl sulfates, alkyether sulfates, sulfated alkanolamides, alpha olefin sulfonates, lignosulfonates, sulfosuccinates, fatty acid salts, and phosphate esters. Examples of cationic surfactants include alkyltrimethylammonium salts.

In one instance, the cellulosic material is prepared as a treated cellulosic material by pressure treatment. The pressure used to pressure treat the cellulosic material may be either higher or lower than atmospheric pressure. In one instance, the pressure is lower than ambient pressure, for example, 0.0001 to 0.09 MPa (0.75 to 675 mmHg). In another instance, the pressure is greater than ambient pressure, for example, 0.1 to 1.7 MPa (750 to 12750 mmHg). It is envisioned that pressure treatment processes known in the art are suitable for impregnating the cellulosic material with the treating agent.

In one instance, the treated cellulosic material is prepared according to at least a first treatment protocol and a second treatment protocol. In one instance, the first treatment protocol comprises impregnating the cellulosic material with the polymer. The first treatment protocol comprises one or more of the following steps: (a) depositing the cellulosic material in a vessel; (b) holding the vessel at vacuum for 5 to 60 minutes; (c) introducing the polymer to the vessel; (d) pressurizing the vessel to 1.03 MPa for 5 to 60 minutes; (e) draining the excess polymer; (f) optionally removing excess polymer by vacuum; and (g) air drying the cellulosic material at 20 to 60° C. for 24 to 48 hours. In one instance, the polymer is part of the aqueous dispersion.

In one instance, the product of the first treatment protocol is subsequently prepared according to a second treatment protocol that impregnates the cellulosic material with the modifying agent. The second treatment protocol comprises one or more of the following steps: (a) depositing the cellulosic material prepared according to the first treatment protocol in a vessel; (b) introducing the modifying agent to the vessel; (c) holding the vessel at either vacuum or increased pressure for 5 to 60 minutes; (d) optionally removing excess modifying agent by vacuum; and (e) air drying the cellulosic material at 60° C. for 24 to 48 hours.

The several drying steps may be performed at a range of temperatures, whereby the duration of the air drying step is proportional to the temperature. Suitable air-drying temperatures are between room temperature (roughly 20° C.) and 180° C. The drying may be performed in air, in nitrogen, or other suitable atmosphere.

A water immersion test is used to determine the water repellency of the treated cellulosic material according to the American Wood Protection Association Standard E4-11 procedure (Standard Method of Testing Water Repellency of Pressure Treated Wood). The water immersion test involves first, providing both a treated wafer, comprising a treated cellulosic material prepared as described herein, and a control wafer, comprising a cellulosic material treated according to the first treatment protocol described herein except that the dispersion is replaced by distilled water; second, measuring the tangential dimension of both the treated wafer and the control wafer to provide an initial tangential dimension (T₁) (where the tangential dimension is perpendicular to the direction of the grain of the cellulosic material); third, placing both the treated wafer and the control wafer in a conditioning chamber maintained at 65±3% relative humidity and 21±3° C. until a constant weight is achieved; fourth, immersing both the treated wafer and the control wafer in distilled water at 24±3° C. for 30 minutes; and fourth, measuring the tangential dimension of both the treated wafer and the control wafer following removal from the water to provide a post tangential dimension (T₂).

DoN refers to the degree of neutralization of the carboxylic acid functionality in the polymer.

The percent swelling (S) for each individual wafer (both the treated wafer and the control wafer) is calculated as:

${S(\%)} = {\frac{T_{2} - T_{1}}{T_{1}} \times 100}$

In each of the Examples herein, the percent swelling of the control wafer is 4.7%.

Water-repellency efficiency (WRE) is used to determine the effectiveness of the treating agent in adding water repellant properties to the treated cellulosic material. WRE is calculated as:

${{WRE}(\%)} = {\frac{S_{1} - S_{2}}{S_{1}} \times 100}$

S₁ refers to the percent swelling of the untreated wafer; S₂ refers to the percent swelling of the treated wafer. According to E4-11, for most outdoor applications a minimum WRE of 75% is preferred. The WRE of raw wood without any treatment is 0%.

The hardness of the treated cellulosic material is determined according to the Shore (Durometer) test using a Type D Durometer (30° cone, 1.40 mm diameter, 2.54 mm extension, 44.48N spring force). Hardness is determined using the Type D Durometer by placing the cellulosic material on a hard flat surface, and the foot of the Durometer is pressed with the given spring force against the cellulosic material. The hardness value is recorded from the gauge on the Durometer within one second of contact with the cellulosic material. At least five hardness tests were performed per sample of cellulosic material. Hardness values reported herein are averages of the tests performed for a given cellulosic material. The hardness value of an untreated wafer is 40.

Termite resistance of the treated wood is determined by preparing two groups of eight samples, the first group of samples comprise eight wafers of wood prepared according to a particular treatment regime (test samples), the second group of samples comprise eight wafers of untreated wood (control samples). Each of the samples are prepared by first drying the samples at 49° C. for 24 hours. The samples are then weighed. Two colonies of termites (Reticulitermes flavipes, four treatment replicates per colony, 100 workers per replicate) were placed in a Conviron growth chamber (Model CG72) held at 28° C. and 60 percent relative humidity and held for seven days. After seven days, termite wood resistance is observed by comparing consumption of samples and termite mortality of the test samples to the control samples. In the cases where survivorship of the termites remained high after the first seven days, the samples and termites were returned to the Conviron for seven additional days and subsequently evaluated.

The following Examples illustrate certain aspects of the present disclosure, but the scope of the present disclosure is not limited to the following Examples.

The dispersions in the following Examples were made by combining the polymer with the given amount of base in a mixed, pressurized vessel at 120° C. as is known in the art (for example, a suitable dispersion may be prepared according to “Preparation of Aqueous Dispersions of PRIMACOR Copolymers” from The Dow Chemical Company). All the vacuum operations in the examples are in the range of −0.00399 MPa to −0.00267 Mpa. All the vacuum operations in the examples are in the range of 0.00399 MPa to 0.00267 MPa.

EXAMPLE 1

A pine wafer (southern yellow pine, 4 cm×2 cm×0.5 cm) is held at the bottom of a Parr reactor by a weight (here a ring is used). The reactor pressure is set to vacuum for 30 minutes. 80 ml of a dispersion comprising 20 percent by weight Primacor 5980 (50% DoN with MEA, 8.21 pH, particle size of 117 nm) and 80 percent by weight water is introduced to the reactor. The reactor pressure is then set to 1.03 MPa for 60 minutes under nitrogen. The wafer is then placed in an oven and air dried at 60° C. for 48 hours. The wafer is held at the bottom of the reactor by the weight. The reactor is filled with sufficient trimethyl soya alkyl ammonium chloride solution (50% actives in isopropanol and water, Davies HLB 20.8, sold as Arquad SV-50 by Akzonobel) to submerge the wafer. The reactor pressure is set to vacuum for 60 minutes. The wafer is then placed in an oven and air dried at 60° C. for 48 hours, thereby providing a treated wafer. The first piece of the wafer and the control wafer are each processed according to the E4-11 procedure. The percent swelling for the first piece of the wafer is 1.5%; the WRE of the first piece of the wafer is 66.67%. The hardness of the treated wafer is measured as 37.6 using a Type D Durometer. The termite resistance test: the control sample consumption is 70.63 mg, and the test sample consumption is 1.72 mg.

The Example illustrates that when the cellulosic material contains the treating agent, including both the polymer and the modifying agent, favorable WRE results are obtained. However, where the cellulosic material has not been treated by both the polymer and the modifying agent, favorable WRE results are not obtained. The Example further illustrates that the treated cellulosic material exhibits improved termite resistance as compared to untreated wood. 

What is claimed is:
 1. A method for preparing a treated cellulosic material comprising: (a) providing a cellulosic material, wherein the cellulosic material is wood; (b) a first treatment protocol comprising impregnating the cellulosic material with an aqueous dispersion comprising a polymer, the polymer comprising an olefin-carboxylic acid copolymer; and (c) a second treatment protocol comprising impregnating the cellulosic material with a modifying agent, the modifying agent comprising a quaternary ammonium compound, wherein the second treatment protocol is a discrete processing step separate from the first treatment protocol.
 2. The method of claim 1, wherein at least a portion of the carboxylic acid groups of the olefin-carboxylic acid copolymer are neutralized.
 3. The method of claim 1, wherein the olefin-carboxylic acid copolymer comprises, in polymerized form, a monomer selected from the group comprising ethylene, propylene, 1-butene, 3-methyl-1-butene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-heptene, 1-hexene, 1-octene, 1-decene, 1-dodecene, butadiene, styrene or a mixture thereof.
 4. The method of claim 1, wherein the olefin-carboxylic acid copolymer comprises, in polymerized form, a carboxylic acid monomer or anhydride monomer selected from the group comprising acrylic acid, maleic acid maleic anhydride, or a mixture thereof.
 5. The method of claim 1, wherein the quaternary ammonium compound is of the formula R¹R²R³R⁴N⁺X where each R¹, R², R³, and R⁴ independently is alkyl, alkenyl, alkynyl, cycloalkyl, aryl, or any combination of these, and the anion X is chloride, bromide, iodide, borate, carbonate, bicarbonate, nitrite, or a carboxylate, such as acetate, laurate or stearate, or a combination thereof.
 6. The method of claim 1, wherein the quaternary ammonium compound is alkyl trimethyl ammonium chloride with C12-C18 alkyl groups, didecyldimethylammonium chloride, dialkydimethylammonium chloride with C8-C14 alkyls, alkyldimethylbenzyl ammonium chloride, or alkyl benzyldimethylammonium with C12-C18 alkyl groups, or a mixture thereof.
 7. The method of claim 1, wherein the modifying agent is trimethyl soya alkyl ammonium chloride.
 8. The method of claim 1, wherein the polymer is ethylene-acrylic acid copolymer.
 9. The method of claim 1, wherein the impregnating of the first treatment protocol is conducted under pressure greater than or lower than ambient. 